Cellular printing plate and method of manufacture thereof



A. MURRAY 2,543,046

CELLULAR PRINTING PLATE ANDMETHOD OFMANUFACTURE THEREOF Feb. 27, 1951 Filed May 21, 1947 FIG. 1. a

FIG. 7.

ETCH/NG AND REMOVING RES/ST INVENTOR ATTORNEY (3 AGENT ALEXANDERMURRAY Patented Feb. 27, 1951 CELLULAR PRINTING PLATE AND METHOD OF MANUFACTURE THEREOF Alexander Murray, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application May 21, 1947, Serial N0. 749,446

1 Claim. 1

This invention relates to printing plates and specifically to an improved form of the so-called Glassey block described in copending application, Serial Number 745,019, filed April 30, 1947 by C. Q. Glassey.

Cross reference is also made to my concurrently filed application, Serial Number 749,447, having to do with an improved method of printing with such plates. A plate according to the present invention is particularly useful with said improved method. r

The object of the present invention is to provide a modified form of Glassey block which will permit more rapid printing. According to the invention the block is made up with cells Whose main or wide portion extends almost all the way through the cellular sheet and which have only a short narrow orifice between this main portion and the front surface of the printing plate. For the sake of definiteness it is pointed out that the diameter of the main portion of each cell is between 1 and 2 times its depth, the rear of each cell is substantially fully open to the surface of the cellular sheet, but in accordance with Glasseys invention it is closed by a transparent layer which covers the whole of the cellular sheet, at least during the actual printing step. The diameter of the orifice is less than 6 the distance between adjacent orifices for the sake of good image quality in the high lights of the final print since it is not possible to make a finite dot smaller than the diameter of this orifice. B way of defining the depth to which the main portion of the cell extends, it is pointed out that the length of the orifice between this main portion and the printing surface of the sheet is less than the thickness of the sheet; it is also less than 5 times the diameter of the orifice, which constitutes one essential feature of the present invention compared to the original Glassey block. The cells are most efiicient when they cover as much as possible of the cellular sheet, but of course this reduces the strength of the sheet. However, the thickness of the walls between adjacent cells at the thinnest place is in general less than the average diameter of the main portion of each cell.

A second essential feature of a printing plate according to the present invention is the use of a material such as metal or a plastic containing a black pigment so that the plate itself absorbs radiation during printing and thus aids in rapidly heating the cells. The large size of the individual cells, the shortness of the exit orifice from each cell and the rapid heat absorption by the walls of the cells all tend to speed up the printing operation which, as described in the above mentioned Glassey case, involves the expulsion of ink from the cells due to thermal expansion when a radiant energy image is incident on the cells.

Further according to the invention, the above described printing plate can be made by etching, using materials well known in the photo-etching art. The rear surface of the sheet of material to be etched is provided with a resist arranged according to a halftone pattern. This is done by well known methods involving exposure of a photoreslst through a halftone screen and processing the resist to leave a screen stencil with spots of the etchable material exposed. The sheet is then etched, with occasional application of dragons blood if necessary to prevent undercutting, until the cavities in the sheet created by the etching, extend almost but not quite through to the other side of the sheet. A photoresist is then applied to the front surface of the sheet and exposed through the sheet from the etched or cavity side. The material of the sheet is transparent to the exposing radiation but has a density proportional to its thickness. In the case of metal foil, X-rays may be used as the exposing radiation. The exposure of the photoresist is a maximum at the point where each cavit is deepest and the remaining thickness between the cavity and the front surface of the sheet is minimum. The resist is then processed to expose these tiny spots corresponding to the deepest point of each cavity. A quick etch is then applied which forms a tiny orifice through from the front surface of the sheet to each cavity which now constitutes the cell of the printing plate. The solutions and resist are then all removed and a printing plate of the type above described is obtained.

The operation of the invention will be fully understood from the following description when read in connection with the accompanying drawing, in which:

Fig. l is a greatly enlarged cross section of a part of a cellular plate according to the teachings of Glassey.

Fig. 2 similarly illustrates a plate according to the present invention.

Figs. 3 to 7 constitute a flow chart for a method of manufacturing such a cellular plate.

Fig. 8 is a rear view of the plate shown in Fig. 7.

In Fig. 1 a cellular printing plate I0 is made up of cells I l each having an orifice M to the front surface of the plate and each being substantially open to the rear surface. In the Glassey printing system these cells are filled with ink and the relatively large rear apertures of the cells are closed by a transparent sheet laidfirmly over the rear surface of the plate M. A radiant energy image negative to that to be printed is then allowed to impinge on the, rear; surface of the ia't'eausing theink in the cells 'to expand and to be expelled through the orifices l2 to print on to a sheet of paper or other material placed in contact with the front surface of the plate. The rapidity of operation of this step depends on the rate at which heat is absorbed by the ink in the cells and on the speed with which it can .be forced through the orifice l2.

According to the invention both of these characteristics are improved as shown in Fig. 2. The material constituting the printing plate i3 is made to absorb the radiant energy and to transfer it rapidly to the ink in the cells. This is done by making the material l3 of metal or by making it of plastic with a black pigment such as particles of metal embedded therein. This rapid 21 to a support 28. The front surface of the sheet 25 which is eventually to be the rear surface of the printing plate, is provided with a resist 26 in the form of a halftone pattern. This resist may be prepared in situ by any of the standard photoresist methods involving exposure absorption and transfer of ink does not have any appreciable adverse effect on the quality of the image since the transfer is from the material I3 to the adjacent cell during each printing cycle and there is not sufficient time for this heat to travel to more distant cells. It should be noted that the rate of heat absorption and the rate of heat transfer are the characteristics to be augmented rather than the heat capacity. It is desirable to keep the heat capacity relativel low so that the maximum amount of heat goes to the ink. Thus the non-conducting materials with a black or other heat absorbing pigment therein have an advantage over the metal foils, but the rate of heat transfer is also somewhat less. Another factor which is considered is the thermal expansion of the material i3 itself, but this factor appears to be of minor importance probably because the effects thereof tend on one hand to reduce the ink expulsion but on the other hand to increase it.

The most important feature of the present invention is the fact that the main portion 14 of each cell has a depth I! only slightly less than the thickness of the sheet l3. The diameter ii of each cell may be anywhere from the depth i! to twice this depth. That is, the diameter of the cells is of the same order as their depth. Since the cellular plate works most efficiently when the cells cover most of the area of the plate, the thickness i8 between adjacent cells should be less than the diameter i6 and should be as thin as is commensurate with suitable strength in these walls between cells. The orifice i5 from each cell to the printing surface is narrow and according to the invention it has a length less than 5 times its diameter whereas the prior blocks had this length i9 somewhat greater than 5 times the diameter. Since the orifice I5 is very narrow, the length thereof also turns out to be less than /5 the thickness of the sheet l3. As shown in Fig. 2 the most preferred form of plate has the length of the orifice I5 approximately equal to its diameter.

In Fig. 3 a sheet of etchable material. is temporarily mounted by a strippable adhesive Number through a halftone screen of" the desired fineness, and processing to leave cavities between crossed lines of resist.

The sheet 25 is then etched forming cavities 29 therein and the etched sheet 30 is transferred with the strippable layer 21 and is mounted face down on a second temporary support 38. During the etching operation between Figs. 3 and 4, dragon's blood is applied when necessary to keep the etching solution from under-cutting the sheet.

In Fig. 5 a photoresist layer is then applied to the back of the sheet 30 and light from a lamp 31 exposes this photoresist through the sheet 30. The density of the sheet 30 is of course proportional to its thickness and therefore the resist 35 receives its greatest exposure at the points opposite the deepest part of each cavity. Even with some metal foils it is possible to expose using intense ordinary light, but X-rays are used when necessary for this exposure. The resist layer is then processed to leave tiny spots exposed opposite to each cavity and thus to form a stencil 38. A quick etch is then applied which forms a tiny orifice 39 through the thinnest point in the sheet 30 connecting with each of the cavities 29. The removal of the resist leaves the required printing plate illustrated in Figs. 7 and 8. The invention is not limited to the details of the above structures and processes but is of the scope of the appended claim.

I claim:

The method of preparing a cellular printing plate, which comprises placing a resist stencil in halftone pattern on a surface of a sheet of etchable material which transmits actinic radiation but has a density with respect thereto proportional to its thickness, etching the halftone spots of the sheet left exposed by the stencil, terminating the etching when the cavities thereby created are nearly but not quite through the sheet, applying a photoresist to the other surface of the sheet, exposing the latter resist to actinic radiation through the sheet, processing the latter resist to expose a small spot of said other surface over each cavity at the point where maximum actinic exposure due to minimum thickness of the sheet material occurs, and etching a narrow orifice at each spot through to the corresponding cavity.

ALEXANDER MURRAY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 378,423 Baynes Feb. 28, 1888 1,319,076 Hermann Oct. 21, 1919 1,889,543 Coors Nov. 29. 1932 

